There is a need for coatings for oven bake clay that are food and drink safe.
Ceramics are used to make a variety of objects. These include industrial and home applications. Among the home applications are artistic creations and other household items as well as items used for eating and drinking, such as plates, cups, bowls, and serving pieces. Ceramics have the advantage that they can be coated with glaze and fired at high temperatures. Many readily available glazes are certified for use with foods and drinks. Glazes work by forming a non-porous glass-like coating that seals any toxic materials in the clay and reduces porosity. The non-porous, smooth surface avoids creating an environment where potentially harmful microorganisms can grow and reduces the potential for liquids to erode the underlying clay.
The issue with ceramics and with glaze is that they require firing in a kiln. Kilns are expensive, require specialized training and are not readily available in most homes.
As a result, modeling clays have been developed so that those without access to a kiln can make similar objects. Modeling clays include several sub-types: oven bake clays, oil-based clays and paper or air-dry clays. Oven bake clays are made of polymers such as polyvinyl chloride (referred to as polymer clays) or crystalline silica. Brands of oven bake clays include Sculpey, Fimo, Cernit, Premo, Modello, Du-Kit, Kato Polyclay, Formello, Friendly Clay, Artist's Modelene, Jack Johnston's Clay, Prosculpt and Laguna Clay. Most of these oven bake clays are made of polyvinyl chloride and are baked at 250 degrees to 300 degrees Fahrenheit. Laguna Clay is made of crystalline silica and is baked at 350 degrees Fahrenheit. In addition, various home made formulations have been developed that generally include flour and water. While not as durable as commercially available oven bake clays, these formulations can be hardened in the oven at similar temperatures or air-dried. Generally, oven bake clays can be hardened to a greater extent than other modeling clays and are more durable once baked. Paper or air-dry clays harden when exposed to air and oil-based clays remain more malleable even after exposure to air.
These various types of modeling clays are useful for making artistic creations but cannot be employed in making food and drink safe items. This is because there are no coatings for these products that seal in the toxic materials and form a smooth, non-porous surface. A smooth, non-porous surface is necessary to prevent the growth of microorganisms and to prevent erosion by liquids as well as to seal in toxic materials. Conventional glazes cannot be used on modeling clays because the glassification process requires temperatures well over 1000 degrees Fahrenheit. At these temperatures, these various types of modeling clay products would burn and in some cases would release toxic fumes and toxic breakdown products.
Therefore, there is a need for a composition that can be used over modeling clays to form a smooth, non-porous coat and hence food and drink safe coating at lower temperatures. In particular, there is a need for such a composition that can be used at less than 1000 degrees Fahrenheit and preferably less than 500 degrees Fahrenheit, and most preferably less than about 400 degrees Fahrenheit or 300 degrees Fahrenheit. These are temperatures that can be achieved in a home oven or toaster oven and that do not burn the polymer clay or cause the release of excessive toxic fumes or breakdown products.
A number of the manufacturers of modeling clays make glazes for decorative purposes. These glazes are designed to change the appearance to a gloss or matt finish or change the color of the modeling clay. These glazes do not require baking but also are not food and drink safe. They are generally made of polyurethanes. These materials do not provide the seal, durability and smooth surface required for designation as food and drink safe.
Jeanne A. E. DeVoto (http://www.jaedworks.com/clayspot/polyclay-faq/finishing.html) has suggested the use of products such as Flecto Varathane Elite Diamond Finish (polyurethane based) and Future floor polish (styrene/acrylic copolymer based) both of which are not designed to provide a food and drink safe coating but instead may be used as a less expensive alternative to decorative glazes sold by manufactures of oven bake clay.
Eileen Bergen (http://www.theartfulcrafter.com/blog/polymer-clay-two.html) has suggested a food and drink safe coating for polymer clay using carnauba wax or shellac NF. While she suggests that these materials are themselves food safe, she does not describe attempting to glaze polymer clay using these materials and has not demonstrated that they can provide a sealed, smooth, non-porous surface over these materials.
Several patents describe coatings for modeling clays or, alternatively, food safe coatings. However, none of these patents describe a food safe coating for oven bake clay. Spector Herman describes a method of coating oil-based clays in “Process for coating modeling clay and product produced thereby” US Patent Publication number U.S. Pat. No. 3,558,340 A. However, his inventions do not pertain to oven bake clay, and his invention is focused on hardening oil-based clay rather than providing a food safe surface. Isoya Mamoruwpo describes in World Intellectual Property Organization publication number 10099196 a method for coating ceramic using silver ion as an antibacterial. However, his coating is for use over conventional ceramics, not oven bake clay, and requires heating to 1472 degrees Fahrenheit (800 degrees Celsius), a temperature that is too high for use with oven bake clay.
There is a need for a coating that can be used over oven bake clay that provides a reliable smooth, non-porous food and drink safe coating that is durable and long lasting.